WASHINGTON (AP) -- Once again, Hillary Rodham Clinton did it her way, and it could cost her.
Clinton's decision to eschew government email and use her own private server as secretary of state is raising questions about secrecy, security and the law -- including whether she might have deleted important messages tapped into her ever-present BlackBerry instead of preserving them for public scrutiny and history.
At the least, the controversy is a bump on her unprecedented path from first lady to presumed presidential contender.
What we know so far:
WHAT'S DIFFERENT ABOUT CLINTON'S EMAIL?
She did all her official work as the nation's top diplomat using a personal email account. Federal officials are generally expected to use their agencies' email systems -- the kind of addresses that have ".gov" at the end.
Clinton didn't use a commercial email server, like Google operates for Gmail, either. She had her own email server, traced to her hometown in Chappaqua, New York. The address: email@example.com.
Prior secretaries of state also used nongovernment email for work at times, or avoided using email much at all. Indeed, the State Department says the current secretary, John Kerry, is the first to have an official "@state.gov" address like other employees use routinely.
The volume of the Clinton documents -- she's turned over 55,000 pages -- makes her use of personal email more striking.
IS SOMETHING WRONG WITH WHAT SHE DID?
It raises two opposing sets of questions:
-- Was Clinton's email too secret?
A private account could have allowed her to withhold or destroy messages that she's legally required to turn over for congressional investigations or lawsuits or to make available to the public, the press and historians under open-records law.
-- Was Clinton's email too exposed?
A private email server may have left her sensitive government communications more vulnerable to people who shouldn't see them, such as hackers and spies, because it lacked the heavy security of government accounts.
The answers are fuzzy.
Clinton says she's turned over all relevant emails to the State Department. The House committee investigating the deadly attack on a diplomatic mission in Benghazi, Libya, has issued subpoenas seeking messages that might not have been divulged.
Clinton hasn't released any information about her email server and its security features. Private email servers are generally not as reliable or secure as those used by the government or in commercial data centers.
Clinton aides and the State Department both say she never received or transmitted classified information on her private account.
DID CLINTON BREAK THE LAW?
That's to be determined. Her aides say no.
Her use of private email appears to conflict with the spirit of Barack Obama's pledge to make his presidency the most open ever. She stands out even in an administration that has been criticized as failing to live up to that promise.
However, Obama didn't sign a law requiring the archiving of officials' emails, including those on private accounts, until last November. Clinton left the State Department two years ago.
Even back when she was in office, according to the White House, it was administration policy for officials to conduct their work on government email accounts. If their work strayed into personal emails, officials were responsible for making sure those messages were preserved for history.
White House spokesman Josh Earnest says the vast majority of administration staffers work on government accounts, which should assure their emails are preserved automatically.
Clinton spokesman Nick Merrill says much of her messaging was email back and forth with her State Department advisers on their government email, so the correspondence was retained on their end. Still, her emails to or from people outside the U.S. government -- foreign officials, for example -- would not be captured in that way.
After the new law was signed last year, the State Department asked Clinton and other former secretaries of state for email records that should be preserved. That's when Clinton turned over the 55,000 pages.
Earnest said that if Clinton did in fact collect all of her personal email that was related to her official government work and turn it over, "that would be consistent with the Federal Records Act. And that's the president's expectation."
Yet only Clinton and her aides decided what to turn over.
That leaves congressional investigators and others to wonder if she might be holding back things the public has a right to see about Benghazi or other topics.
WAS STATE DEPARTMENT POLICY CLEAR?
Clinton's own office instructed State Department employees to avoid doing work by personal email.
A June 2011 cable to employees warned that "online adversaries" were targeting personal accounts of department employees.
The department now says those instructions concerned emails containing sensitive but unclassified information, such as personal information about employees or members of the public, business secrets or asylum applications.
The issue came up again in a 2012 inspector general's report.
The report advised that reliance on "unauthorized information systems increases the risk for data loss, phishing and spoofing of email accounts," as well as the loss of public records. The report criticized Scott Gration, then ambassador to Kenya, for using an outside email system, among several other problems under his leadership. He resigned.
The State Department will review the mountain of Clinton emails for possible public release and for any security breaches. The process could take months, pushing the matter deeper into the 2016 presidential campaign. In a tweet this week, Clinton said she wanted the department to make her emails public as soon as possible.
Congressional Republicans will keep pressing for emails that might shed light on Benghazi or other controversies, with Clinton's potential presidential rivals surely paying rapt attention.
The State Department is already under pressure to produce information under the nation's open records law. It's juggling nearly 11,000 pending requests for various emails, including more than 75 requests for Clinton material filed from 2009 to 2013 by media organizations and others. Associated Press requests for Clinton emails and other documents have been delayed for more than a year; in one instance, four years.
WILL THIS BE A PRESIDENTIAL CAMPAIGN ISSUE?
It seems likely to linger into 2016. The story fits with critics' longstanding portrayal of Clinton as secretive and operating above the rules.
For example, it recalls the mystery of the missing Rose Law Firm records during the presidency of her husband, Bill Clinton.
The billing records for some of her work as a lawyer in Arkansas were subpoenaed in the investigation of the Clintons' Whitewater land deal. The papers were missing for nearly two years before the Clintons said they had unexpectedly turned up in a storage area in the residential portion of the White House.
Clinton was called to testify about the billing records before a federal grand jury -- an inauspicious first for a first lady.
Her name also was sometimes caught up in the ethics and legal controversies during the Clinton presidency that culminated in Bill Clinton's impeachment on perjury and obstruction of justice charges in the Monica Lewinsky scandal.
Recently, she has also faced questions about her family's charitable foundation taking money from foreign governments while she was running the State Department.
WHAT ABOUT POTENTIAL FOES' EMAILS?
Jeb Bush, expected to seek the presidency on the Republican side, also used a personal email account -- firstname.lastname@example.org -- on a personal server, while he was Florida governor.
Florida's public records law is among the nation's strongest. Bush was required to turn over emails related to his work as governor from 1999 to 2007 to the state archives, making them public.
In a show of transparency, Bush obtained those emails from the archivist and posted more than 275,000 online at jebemails.com last month.
In an example of how tricky public records issues can be, the vast email cache made public included some Floridians' birthdays and Social Security numbers. A spokeswoman said people's private information was removed from the website after it was discovered.
But like Clinton, Bush did not turn over what he determined to be personal messages on his account.
Democrats are raising the same questions about Bush that are being asked of Clinton: How can the public be sure that he turned over all relevant emails from his time in office?
Though Bush has taken a couple of swipes at Clinton over her emails, criticism from Republican presidential hopefuls has been muted so far, perhaps because it is a sensitive issue for several of them.
Email from Wisconsin Gov. Scott Walker and New Jersey Gov. Chris Christie, for example, has become part of criminal investigations.
ONE LAST QUESTION: WHO HAS THEIR OWN EMAIL SERVER, ANYWAY?
Anybody could, but it's a pretty geeky pursuit.
A private server doesn't take a lot of room or a special power source. It could be the size of your desktop computer and sit unobtrusively in your home.
Some people set them up as a techy hobby. Others acquire them for privacy, because they don't trust corporate email providers to keep their messages out of the hands of hackers or government snoops.
Clinton might also have been worried about leaks. Now she says she wants her emails out there.
Associated Press writers Jack Gillum, Ted Bridis, Nedra Pickler, Julie Pace, Anne Flaherty, Thomas Beaumont and Stephen Braun contributed to this report.